Writing instrument



FIG. 1 is a rear view of a writing instrument of my new design;

FIG. 2 is a left side view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is a top plan view thereof.

The broken lines showing the bottom and top are included for the purposes of illustrating environment and form no part of the claimed design. 

The ornamental design for a writing instrument, as shown and described. 